Hello, Try
tapply(tab$S1, tab$time, function(x) length(unique(x))) Hope this helps, Rui Barradas Citando Ashta <sewa...@gmail.com>: > Hi Bert and all, > I have related question. In each time period there were different > locations where the samples were collected (S1). I want count the > number of unique locations (S1) for each unique time period . So in > time 1 the samples were collected from two locations and time 2 only > from one location and time 3 from three locations.. > > tab <- read.table(textConnection(" time S1 rep > 1 1 1 > 1 2 1 > 1 2 2 > 2 1 1 > 2 1 2 > 2 1 3 > 2 1 4 > 3 1 1 > 3 2 1 > 3 3 1 "),header = TRUE) > > what I want is > > time S1 > 1 2 > 2 1 > 3 3 > > Thank you again. > > On Sat, Nov 21, 2015 at 1:30 PM, Ashta <sewa...@gmail.com> wrote: >> Thank you Bert! >> >> What I want is at least 500 samples based on random sampling of time >> period. This allows samples collected at the same time period are >> included together. >> >> Your script is doing what I wanted to do!! >> >> Many thanks >> >> On Sat, Nov 21, 2015 at 1:15 PM, Bert Gunter <bgunter.4...@gmail.com> wrote: >>> David's "solution" is incorrect. It can also fail to give you times >>> with a total of 500 items to sample from in the time periods. >>> >>> It is not entirely clear what you want. The solution below gives you a >>> random sample of time periods in which X1>0 and the total number of >>> samples among them is >= 500. It does not give you the fewest number >>> of periods that can do this. Is this what you want? >>> >>> tab[with(tab,{ >>> rownums<- sample(seq_len(nrow(tab))[X1>0]) >>> sz <- cumsum(X2[rownums]) >>> rownums[c(TRUE,sz<500)] >>> }),] >>> >>> Cheers, >>> Bert >>> >>> Bert Gunter >>> >>> "Data is not information. Information is not knowledge. And knowledge >>> is certainly not wisdom." >>> -- Clifford Stoll >>> >>> On Sat, Nov 21, 2015 at 10:56 AM, Ashta <sewa...@gmail.com> wrote: >>>> Thank you David! >>>> >>>> I rerun the your script and it is giving me the first three time periods >>>> is it doing random sampling? >>>> >>>> tab.fan >>>> time X1 X2 >>>> 2 2 5 230 >>>> 3 3 1 300 >>>> 5 5 2 10 >>>> >>>> On Sat, Nov 21, 2015 at 12:20 PM, David L Carlson >>>> <dcarl...@tamu.edu> wrote: >>>>> Use dput() to send data to the list as it is more compact: >>>>>> dput(tab) >>>>> >>>>> structure(list(time = 1:8, X1 = c(0L, 5L, 1L, 0L, 2L, 3L, 1L, >>>>> 4L), X2 = c(251L, 230L, 300L, 25L, 10L, 101L, 300L, 185L)), >>>>> .Names = c("time", >>>>> "X1", "X2"), class = "data.frame", row.names = c(NA, -8L)) >>>>> >>>>> You can just remove the lines with X1 = 0 since you don't want >>>>> to use them. >>>>>> tab.sub <- tab[tab$X1>0, ] >>>>> >>>>> Then the following gives you a sample: >>>>>> tab.sub[cumsum(sample(tab.sub$X2))<=500, ] >>>>> >>>>> Note, that your "solution" of times 6, 7, and 8 will never >>>>> appear because the sum of the values is 586. >>>>> >>>>> David L. Carlson >>>>> Department of Anthropology >>>>> Texas A&M University >>>>> >>>>> -----Original Message----- >>>>> From: R-help [mailto:r-help-boun...@r-project.org] On Behalf Of Ashta >>>>> Sent: Saturday, November 21, 2015 11:53 AM >>>>> To: R help <r-help@r-project.org> >>>>> Subject: [R] Conditional Random selection >>>>> >>>>> Hi all, >>>>> >>>>> I have a data set that contains samples collected over time. In >>>>> each time period the total number of samples are given (X2) The goal >>>>> is to select 500 random samples. The selection should be based on >>>>> time (select time periods until I reach 500 samples). Also the time >>>>> period should have greater than 0 for X1 variable. X1 is an indicator >>>>> variable. >>>>> >>>>> Select "time" until reaching the sum of X2 is > 500 and if >>>>> X1 is > 0 >>>>> >>>>> tab <- read.table(textConnection(" time X1 X2 >>>>> 1 0 251 >>>>> 2 5 230 >>>>> 3 1 300 >>>>> 4 0 25 >>>>> 5 2 10 >>>>> 6 3 101 >>>>> 7 1 300 >>>>> 8 4 185 "),header = TRUE) >>>>> >>>>> In the above example, samples from time 1 and 4 will not be selected >>>>> ( X1 is zero) >>>>> So I could reach my target by selecting time 6,7, and 8 or time 2 and >>>>> 3 and so on. >>>>> >>>>> Can any one help to do that? >>>>> >>>>> ______________________________________________ >>>>> R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see >>>>> https://stat.ethz.ch/mailman/listinfo/r-help >>>>> PLEASE do read the posting guide >>>>> http://www.R-project.org/posting-guide.html >>>>> and provide commented, minimal, self-contained, reproducible code. >>>> >>>> ______________________________________________ >>>> R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see >>>> https://stat.ethz.ch/mailman/listinfo/r-help >>>> PLEASE do read the posting guide >>>> http://www.R-project.org/posting-guide.html >>>> and provide commented, minimal, self-contained, reproducible code. > > ______________________________________________ > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.htmland provide commented, > minimal, self-contained, reproducible code. [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.